Cycle News - Archive Issues - 1970's

• • • Bow Ihe Iwo-slroke engine gol fasl I II I II ..:lI E -e- f" O'l ~ .-.. c C'J - .( .... This 1935 NSU 200cc model was typical of two-strokes before the war. The NSU was a cheap utility model with an infer ior performance. a QQQ By Geoffrey Wood In the history of two-stroke engine design there are several especially significant innovations. that are responsible for the current CASH and CONTINGENCIES! ij 31 ~. dominan ce oftwo-st rokes in both racing and roa dste r use. On e of these is th e loop scavengi ng principle inven ted b y Dr. Schurle at the FIRST RACE AT 12:00 noon 9 SEE more thaD TOP PIOS induding all the laetory teams! Pierre Karsmakers Gary Jones Jim O'Neal Mike Runyard Rich Thorwaldson Randall Berkeley. Jr. J im Weinert Peter Lamppu Terry Bilton Daniel LaPorte Bob Grossi Kenneth Zahrt Richard Franklin 'Gary Chaplin David Messe r Bruce McDougal Rich Eierstedt Gary Semics Eddie Cole Tony Wynn Anthony DiStefano Mitch Mayes Terry Clark Mark Blackwell Jeffrey Vid ic Bruce Baron Bill Clements Marty T ripes AI Baker Rex St aten Billy Payne Bill Grossi Mike Ha rtwig Tim Ha rt Bry ar Ho lcomb Lars La rsson Bill Cook Ron Pomeroy Tom Rapp Chuck Bower Gay lon Mos ier Andy Baine s These riders guaranteed, rain or sh ine! HANG GLIDERS! 60 OF THE HOTTEST OLD TIMERS! BEER! HAMBURGERS! POP CORN! SOFT DRINKS! HOT DOGS! GENERAL ADM iSSI'ON: $5 JUNIORS: $4 under 10 FREE! BAYNARE CYCLE PARK DON'T MISS the th rills and spills on the giant "SENIOR HILL" SEE the action as the top riders battle t he famed " BANZAI HILL" Ventura Fw y. WEST end fw y . Balcom Canyo' l Rd . • • • • :?' • • •• In the late 1950s the East German MZ two-strokes won many GP races with their fast 125 and 250cc models. These bikes used a perfected expansion box exhaust system . , machines. Desp ite bei ng invented by Sir Dugald Clark in Eng lan d in 1881, the t w o -s t ro ke e ngine had n o t been de veloped as much as the m or e co m plex fo ur-stroke design, so th at by the ear ly 19 3 0s it was very much a laugh in g matter in all o f mor orcy cledom . Almost all. T he re we re seve ra l m en who be lie ved th e re w as a fu t ure for th e m o re simple two-stro ke e ngi ne . One of these wa s Dr. Sc h n urle a t the DKW work s in Germany - a fi rm that was tryi ng 10 develop a two-stro ke Grand Prix bike that wo uld be com petitive . T he proble m bac k the n wi th BAYMARE _ _ ... No overn ight camping 34 Hwy.118 '--1--+-.....;......- - - i DKW fac to ry in 19 34, and the second was th e more gradual evo lu ti on of the exp ansion cham ber exhaus t sys te m by Walter Kaad en at th e MZ factory in the m id d le 1950s. With out th ese tw o eng ine ering advance s, the two-stroke would still b e just what it was until these id eas came alo ng - a lo w powered an d unreliab le engine used to power inexpens ive ut ility , Sanctioned by AMA the tw o -s tr oke was that it was neit he r fast no r re liab le. T he lack of speed was due to too much fuel being lost O U I t he exhaust port, and the lack of re lia bi lity was due to th e ra ised p is ton LTOwn th a t wa s u sed in a n e ffo rt to prevent the in coming fuel cha rge . . .. .. . ...-. . .. from traveling straight out th e exhaust port. DK W fo und that th e pi ston wo uld always seize du rin g a long, hard ra ce, s i nce t he d ist orted piston sha pe exp an de d unevenl y and expanded so much th at a seizure wa s ine vita ble. In an effort to solve , t his thorn y problem, Dr. Sc hnurle lab ored long an d hard. He was finally successful in 1934 w he n he devised the loop sca veng ing theory, and this id ea must surely ra te as th e mos t s ig nifica n t i m p ro vem en t for the two-stroke in its en ti re h istory , In Dr . Sc h n ur le's engine, t he tran sfer ports were moved fro m their lo cat io n at the rea r of th e cylinde r to th e fron t wal ls. Th ey wer e a lso inclined up wa rd s, so tha t th e p ort shape , ra th er th an p iston shape, co n trolled th e in ternal flow o f the incomi ng fue l charge. The p ist on cro wn cou ld then be left ne arly fla t. T his design had t he ad vantage th a t t he cool incomi ng fuel -air charge crossing th e p isto n crown w ould co o l it , and the eve nly shaped p ist on ex p an ded un ifo rm ly so t h us would not be as ap t to seize. T he in co mi ng fuel charge the n traveled up t he back wall of the cylinder an d lo o ped over the to p , to con t inue its travel down the front wal l to pass out the ex haust po rt. In 19 3 4. DKW fiel ded a new 25 0cc road racer fea turin g th is loop scaven gin g design, bu t it was not un til 19 3 5 t hat the y a chieved succe ss. Arth ur Gei ss won the 250cc European Cha mpionshi p that year with a water -cooled spli t-sin gle tha t d eveloped 25 HP at 440 0 RPM. In 1936. he returned wi th an even fas ter model producing 30 HP a t 6000 R PM. The new Deek use d a ro ta ry inlet valve in place o f th e ea rlier reed valve , b ut it ret a ined a pis ton-type su pe rch arge r. T he pr e-war DKW s domi nated the 25 0<:c class, and in 19 3 9 th ey ca me within a whisker of defeatin g th e fast Ve locette fou r-st rok es wh ich had a lar ger 35 0c c eng ine wi th o ver head cam. In 1939 the pist on co m p resso r wa s drop p ed in fa vo r o f an eccent ric vane supe rc ha rger. This booste d p ow er 10 40 and 56 HP o n the l~VO m od els. Su percharging was o utlawed by the F . l.~ l. a fter the wa r, and the two -stroke was relega te d ba ck to bei ng a n also-ran un t il the m iddle 1950s wh en DK\\' again re t urned wi th an exo ti c racer. T his o ne was a 350cc " three" th a t was very fasl 145 MPH - b ut th e bike lacked a wee

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